I'm sure the optimal combination varies from person to person, but my best results came with 30 seconds on, 90 seconds off. I think the sweet spot is for the sprint period to be a few seconds longer than you think you can handle, so that you're really scraping the barrel to get through it, and for the recovery period to be just short enough that you don't quite get back down to the heart rate you had before the sprint.

The clear winner will be whatever works for you. Unfortunately most of these tests are done on either trained athletes or sedentary individuals so the results need to be taken with a grain of salt. I'd start with 20/10 and adjust as needed.